Transformers have become essential electronic components for various electronic devices such as power supply apparatus or power adapters. Since the electronic devices are developed toward small size and high power, the size of the transformers contained in the electronic devices should be minimized. Referring to FIG. 1, a schematic exploded view of a conventional transformer is illustrated. The transformer 1 of FIG. 1 principally comprises a circuit board 11, a plurality of pins 12, a magnetic core assembly 13 and a fixture member 14. The circuit board 11 is for example multi-layered circuit board and has thereon winding coil patterns including a primary winding coil and at least a secondary winding coil (not shown). The circuit board 11 has a hollow portion 111 at the center thereof and a plurality of conductive holes 112. The conductive holes 112 are distributed at bilateral sides of the circuit board 11 and connected to the winding coil patterns. First ends of the pins 12 are inserted and fixed into respective conductive holes 112. Second ends of the pins 12 are connected to corresponding contact pads on a system circuit board (not shown) according to a surface mount technology (SMT), such that the transformer 1 is mounted onto the system circuit board.
Please refer to FIG. 1 again. The magnetic core assembly 13 includes of the transformer 1 includes a first magnetic part 131 and a second magnetic part 132. The first magnetic part 131 includes a first sidewall 1311 and a first middle post 1312. A first indentation 1313 is formed between the first sidewall 1311 and the middle post 1312. The second magnetic part 132 includes a second sidewall 1321 and a second middle post 1322. A second indentation 1323 is formed between the second sidewall 1321 and the second middle post 1322. The first middle post 1312 of the first magnetic part 131 and the second middle post 1322 of the second magnetic part 132 are partially inserted into the hollow portion 111 of the circuit board 11. The circuit board 11 is accommodated within the space between the first indentation 1313 of the first magnetic part 131 and the second indentation 1323 of the second magnetic part 132. When the first magnetic part 131, the second magnetic part 132 and the circuit board 11 are combined with each other, the circuit board 11 is received between the first magnetic part 131 and the second magnetic part 132 and the first middle post 1312 and the second middle post 1322 are partially received in the hollow portion 111 of the circuit board 11.
The fixture member 14 includes at least a resilient clip. The first magnetic part 131 and the second magnetic part 132 have recesses 1314 and 1324, respectively. After the first magnetic part 131, the second magnetic part 132 and the circuit board 11 are combined with each other, the fixture member 14 clamps the recesses 1314 and 1324. Under this circumstance, the first magnetic part 131, the second magnetic part 132 and the circuit board 11 are fixed by the fixture member 14. The resulting structure of the transformer 1 is shown in FIG. 2. Due to an electromagnetic coupling effect generated between the magnetic core assembly 13 and the circuit board 11, voltage conversion is rendered. Moreover, for facilitating fixing the circuit board 11, dispensing adhesive 15 is coated on a small portion of the surface of the second indentation 1323 of the second magnetic part 132, so that the circuit board 11 is attached onto the second magnetic part 132.
The structure of the above transformer 1 still has some drawbacks. For example, since the dispensing adhesive 15 is coated on a small surface of the second indentation 1323 of the second magnetic part 132, the surface of the second indentation 1323 is not smooth. In addition, since the area of the second indentation 1323 of the second magnetic part 132 is small, it is difficult to manipulate the dispensing procedure. As a result, the dispensing adhesive 15 fails to be uniformed spread over the area of the second indentation 1323 and thus the circuit board 11 is not firmly secured to the second magnetic part 132. Under this circumstance, the circuit board 11 fails to lie flat on the second indentation 1323 and the circuit board 11 is tilted with respect to the surface of the second indentation 1323. The tilted circuit board 11 results in unevenness of the pins 12. Therefore, the pins fail to be fixed onto the system circuit board due to the poor wetting property and the poor solderability. Furthermore, after the transformer 1 and the system circuit board pass through a reflow furnace (not shown), the dispensing adhesive 15 is readily subjected to brittleness such that the circuit board 11 of the transformer 1 is not firmly secured to the magnetic core assembly 13. Furthermore, a gap is existed between the circuit board 11 and the surface of the second indentation 1323 and/or between the circuit board 11 and the surface of the first indentation 1313. Since the air contained in the gap is not a good thermally-conductive medium, the heat-dissipating efficiency of the transformer 1 is unsatisfied to meet the increasing power requirement of the power supply apparatus or power adapters.
In views of the above-described disadvantages resulted from the conventional method, the applicant keeps on carving unflaggingly to develop an improved transformer according to the present invention through wholehearted experience and research.